The invention described herein was made at the Lawrence Livermore Laboratory, in the course of, or under Contract No. W-7405-ENG-48 between the University of California and the U.S. Department of Energy.
The invention relates to the fabrication of spherical members, such as inertially imploded targets, and more particularly to a method and apparatus utilizing cold gas jets to form a uniform layer of selected material on the inside of a spherical member having one or more layers or shells.
Various types of targets composed of spherical members containing, for example, deuterium-tritium have been proposed. Such targets may consist of either single or multiple shells, for utilization in inertial confinement systems, for example, wherein the targets are imploded by energy from lasers, electron-beams, and ion-beams.
Prior methods for producing these various types of inertial confinement targets are known in the art, as exemplified by U.S. Pat. No. 3,953,617 issued Apr. 27, 1976 in the name of W. H. Smith et al; U.S. Pat. No. 3,985,841 issued Oct. 12, 1976 in the name of R. J. Turnbull et al; U.S. Pat No. 3,987,590 issued Oct. 26, 1976 in the name of R. R. Chianelli; and U.S. Pat. No. 4,021,180 issued May 3, 1977 in the name of J. A. Rinde et al.
Various inertial confinement systems are known in the art for imploding such targets, as exemplified by U.S. Pat. No. 3,723,246 issued Mar. 27, 1973 in the name of M. J. Lubin; U.S. Pat. No. 3,762,922 issued Oct. 2, 1973 in the name of J. C. Hedstrom; U.S. Pat. No. 3,892,970 issued July 1, 1975 in the name of J. R. Freeman et al; and U.S. Pat. No. 3,899,681 issued Aug. 12, 1975 in the name of E. H. Beckner.
Inertial confinement targets have many applications as set forth in the above-referenced U.S. Pat. No. 3,723,246 to M. J. Lubin, such as providing high temperature plasma for use in linear and/or closed plasma research apparatus, such as stellarators, tokamaks, magnetic mirrors, etc. In addition, plasma produced by inertially imploded targets can be used for providing space propulsion, neutron production, physics studies, etc.
The inertial confinement targets thus far experimentally tested have been primarily composed of a hollow glass shell or microsphere filled with fuel such as DT in gaseous, liquid or solid form. The article "Spherical Hydrogen Targets for Laser-Produced Fusion" by I. Lewkowicz, J. Phys. D:Appl. Phys., Vol. 7, 1974, illustrates a method for filling microspheres with such fuel. Targets utilizing a layer or shell of frozen DT have also been developed, see report UCRL-13814 entitled "Separation of Sphere and Shell Laser Fusion Targets" by K. Kim, 1978, pp. 2-54. One of the problems in fabricating such targets is in forming the layer of DT uniformily as non-uniform thickness of the DT layer produces undesirable results.
One of the most favorable targets uses a uniform layer of DT mixture in a glass microsphere, since such reduces the implosion energy required. Methods and apparatus for producing uniform layers of DT within glass shells are exemplified by copending U.S. patent application Ser. No. 872,284 filled Jan. 25, 1978 in the name of J. R. Miller and Applications Ser. No. 924,335 and Ser. No. 924,336, filed July 13, 1978 in the name of R. L. Woerner, each assigned to the assignee of this application. The referenced copending applications utilize a freezing cell to form and hold a uniform DT layer on the inner surface of a target microsphere, wherein the frozen DT is surrounded by cold helium gas in the freezing cell. The frozen DT is momentarily vaporized by either a light pulse or an electrically generated heat pulse, and then quickly refreezes in a uniform layer by the action of the surrounding cold helium gas.
Advanced inertial confinement experiments will utilize complex cryogenic targets with a uniform frozen deuterium-tritium (DT) layer therein. While the above-referenced applications disclose and claim methods and apparatus for effectively forming one or more layers of DT on the inner surface of spherical members composed of single or multiple spaced shells, the complex targets proposed for advanced experiments also involves non-spaced multiple layers or shells. Thus, fabrication techniques are needed to produce the multiple layer or shell complex targets of either opaque or transparent materials as well as the single or multiple-spaced layer or shell targets.